Error on numeric usernames

db_query of user search fails when user with numeric username is being assigned to a ticket. It could be fixed by changing the logic which checks for input to be UID or USERNAME. It solved my problem by replacing any occurance of is_numeric($node->assigned) by user_load($node->assigned)

Example:

// Autocomplete version
    if (isset($node->assigned) && !is_numeric($node->assigned)) {

change to

// Autocomplete version
    if (isset($node->assigned) && !user_load($node->assigned)) {

this has to be done at several places in support.module code. I don't experience performane issues.
I wish someone could build a patch with a more advanced solution!!!